A conventional feedback amplifier is described in Japanese Patent Laying Open, Kokai No. S57-194613. The feedback amplifier includes an amplifier circuit which amplifies an input signal to provide an output voltage signal. The feedback amplifier is also provided with a feedback circuit to control the level of the output voltage signal. The feedback circuit includes a feedback resistor connected between an input terminal and an output terminal, and a transistor connected in parallel with the feedback resistor. The transistor is applied at the base with a control signal. In response to the control signal, a feedback current flowing through the feedback circuit is controlled, so that the output voltage is controlled.
In the conventional feedback amplifier, to broaden the dynamic range of feedback control, it is required that the control signal is determined based on the input current not to saturate the output voltage. The control signal has to be supplied from an external circuit.